The present invention relates to industrial light curtains which monitor a protective or surveillance field and in particular relates to optical modules that can be used for such a light curtain.
Light curtains which are formed by one or more radiation beams are usually also referred to as light grids or light barriers.
Generally, light curtains detect the movement or intrusion of objects into guarded zones and may provide protection for human operators who are working with machines or other industrial equipment. Some light curtain systems are designed to control and monitor industrial automation processes and are in particular used for verifying assembly processes, counting objects, confirming an ejection process, recognize leading edges of transported goods, recognizing irregular shapes and a lot of other applications, etc.
Safety light curtains employing infrared or visible light beams are used to provide operator safety in a variety of industrial applications. In particular, the operator protection around machinery, such as punch presses, guillotines, molding machines, automatic assembly equipment, coil winding machinery, robot operation, casting operations and the like can be improved by using such light curtains. Conventional light curtains typically employ light emitting diodes (LED) mounting at spaced positions along a transmitter bar at one side of the guarded zone, and phototransistors (PT), photodiodes or photo receivers mounted along a receiver bar at the opposite side of the zone. The LEDs transmit modulated infrared light beams along separate parallel channels to the PTs at the receiver bar. If one or more beams are blocked from penetration by an opaque object, such as the operator's arm, the control circuit shuts down the machine, prevents the machine from cycling, or otherwise safeguards the area.
As mentioned above, such an interruption of the beam can also be used for counting objects or verifying the entrance of goods through defined areas.
Usually, light curtains comprise two optical units, often called bars, sticks or strips, which are formed as to different constructional units, one of the optical units having the function of an emitter and one of a receiver. This dedicated architecture of an emitter and receiver, however, has several drawbacks, for instance the fact that the fabrication costs are high, because each type of optical unit has to be fabricated differently. Consequently, there exist concepts that use an architecture, wherein each optical unit has light emitting elements and light receiving elements at the same time. By providing the optical units with identical optical modules, which can operate as a receiver as well as a transmitter, and by additionally providing plug-in units, which differentiate the particular optical unit in its function as the emitter with, for instance, a test input, or as the receiver with, for instance, the output signal switching devices (OSSD), a particularly cost-effective way of fabricating optical units for a large scale production can be achieved.
Such a modular architecture is for instance proposed in the European patent application EP 11 162 263.5.
Known optical modules, however, often suffer from the problem that the alignment of the optical axis for each of the radiation beams is difficult and that the fabrication of the whole module is expensive and involves a lot of rejections due to defects.
The problem underlying the present invention therefore is to provide an optical module and a fabrication method, whereby a particular cost-effective and reliable fabrication and adjustment of the optical components can be achieved.